1. FIELD OF THE INVENTION
The present invention relates to a low skin irritation detergent composition containing, as an active surfactant ingredient, a monoalkyl phosphate salt.
2. DESCRIPTION OF THE PRIOR ART
As surfactant components of detergent compositions, there have been widely used anionic surfactants such as alkyl sulfates, polyoxyethylene alkyl sulfates, alkylbenzene sulfonates and .alpha.-olefin sulfonates.
It is known that such anionic surfactants are adsorbed and thereby remain on the skin surface to cause dryness and scaling of the epidermis, or skin chapping and roughness, if they are used continually. Thus, skin troubles such as roughness of hands are apt to be caused by the use of detergents. Skin roughness can be a precursor of more severe skin troubles such as housewife's eczema. Thus, there is an urgent need to eliminate this disadvantage.
On the other hand, non-ionic surfactants, unlike anionic surfactants, cause little or no skin roughness. However, their properties as surfactants, such as foaming power and detergency, are far inferior to the corresponding properties of anionic surfactants and it has been unsuitable, for many purposes, to incorporate them as detergent active ingredients into detergent compositions.
Further, although phosphoric ester surfactants have been known as anionic surfactants, the phosphoric ester surfactants heretofore used are merely mixtures of monoand diesters or mixtures of mono-, di- and triesters and, therefore, their water-solubilities are very low and they do not possess adequate deterging and foaming powers. In addition, incorporation of them in detergent compositions is difficult.
Although surfactant compounds to which ethylene oxide has been adducted for improving water solubility have also been known, their foaming and deterging powers are also poor and incorporation thereof in detergent compositions has been difficult.
It has been considered that skin roughness is caused mainly by a skin film removing action due to a defatting action and, therefore, the higher the deterging power of the detergent composition, the stronger is the skin roughening action. Thus, it has been considered that it is impossible to obtain detergent compositions that possess a comparatively excellent deterging power and exhibit a low skin roughening effect. The skin roughness referred to herein signifies dryness and scaling of the epidermal layer and is distinguished from skin irritation indicating inflammatory changes such as redness, papula and edema.
However, after intensive investigations, we have discovered that factors which have an influence on the skin roughness include not only the power of the detergent composition for defatting the epidermis, but also many other factors such as its keratin protein denaturating power, skin lysosome and membrane-weakening power. It is more important that the power of the detergent active ingredient to absorb and remain on the skin epidermal layer has a close relationship to the above factors, because the step of washing the detergent off the skin, in running water, is normally practiced after use of the detergent for cleaning has been completed.
It has been considered, therefore, that the degree of skin roughness can be reduced, while maintaining the deterging properties, provided that the keratin protein denaturation and adsorbing/remaining power of the detergent are reduced while the deterging power is kept strong.
For attaining this object, we have investigated structures of surfactants which can reduce the adsorbing/remaining power on the epidermal layer and the power of denaturating keratin proteins and discovered that it is possible to prepare surfactants having excellent surface active properties and reduced adsorbing/remaining power and keratin protein-denaturating power by introducing therein a phosphate group, in place of the terminal sulfate or sulfonate group of the conventional anionic surfactants.